1,720,985 research outputs found
Motor unit recruitment strategy of antagonist muscle pair during linearly increasing contraction.
No full text
Influence of motor units recruitment and firing rate on the soundmyogram and EMG characteristics in cat gastrocnemius
No full textForce dynamic response of tibialis anterior-ankle joint unit in humans.
No full textThe aim of this study was to estimate the dynamic response of a human muscle joint unit by means of the analysis of the torque signal recorded during electrical stimulation of the tibialis anterior (TA). Ten subjects (age: 23-50 years, 7 males, 3 females) volunteered for the study. The leg was fixed in an ergometer designed for isometric contraction of the ankle dorsiflexors and the detection of the generated torque. The amplitude of a 30 Hz stimulation train administered at the TA motor point was varied sinusoidally, thus changing the number of the recruited motor units, and hence the tension at the tendon, in the same fashion. A sequence of 14 frequencies (0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 Hz) was administered. RESULTS: (a) at the 14 frequencies the sinusoidal responses presented distortions always below 2%; (b) from the Bode plots reporting the average gain attenuation and phase shift at each of the 14 input frequencies, it was possible to model the force dynamic response as the one of a critically damped II order system with two real coincident poles (at 2.04 Hz) and a pure time delay (15.6 ms). The possibility to obtain, by means of the system input-output transfer function, data regarding the in vivo mechanics of the muscle-joint unit may represent a novel tool to investigate the functional features of different muscle groups. It may be useful for designing functional electrical stimulation programs as well as training and rehabilitation procedures
Muscle-joint unit transfer function derived from torque and surface mechanomyogram in humans using different stimulation protocols.
No full textTorque and laser detected surface mechanomyogram (MMG) analysis after electrical stimulation of human tibialis anterior (TA) of 14 male subjects was aimed to: (a) obtain the dynamic response.; of TA muscle-joint unit from a long (LP, about I h) and short (SP, 12.5 s) stimulation protocol; (b) compare the resulting transfer function parameters from the two signals.
The sinusoidal amplitude modulation of a 30 Hz stimulation train (SST) changed the number of the recruited motor units, and hence the isometric torque and the TA surface position in the same fashion. Subject instrumentation and SST amplitude range definition took about 25 min. SP: seven consecutive modulation frequencies (0.4, 6.0, 1.0, 4.5, 1.8, 3.0, and 2.5 Hz). LP: fourteen 5 s long isolated frequencies (0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 Hz), 5 min rest in between, Poles position (Hz) and added delay (ms) for phase correction with respect to the input sine (parameters of a critically damped 11 order system) were: torque 2.44 +/- 0.27 Hz (SP) or 2.32 +/- 0.33 Hz (LP) and 18.3 +/- 2.2 ms (SP) or 17.2 +/- 4.5 ms (LP); MMG 2.28 +/- 0.30 Hz (SP) or 2.30 +/- 0.44 Hz (LP) and 17.4 +/- 5.6 ms (SP) or 17.4 +/- 6.4 ms (LP). Differences were never statistically significant. Conclusion: it is possible to characterise the in vivo mechanics of muscle-joint unit with a short (few seconds) stimulation protocol affordable in clinical environment using both torque and MMG signals
Transients of the force and surface mechanomyogram during cat gastrocnemius tetanic stimulation
No full textThe aim of the study was to investigate the time relationship between force and muscle surface displacement, detected as the surface mechanomyogram (MMG) by a laser distance sensor, in the transient phases of a tetanic stimulation. For this purpose the motor nerve of the exposed medial gastrocnemius of four cats was supramaximally stimulated at 30, 40 and 50 Hz for 9 s. Force was detected by a transducer connected at the distal tendon while MMG was measured after pointing the laser beam at the muscle belly. We found that the MMG always anticipated and trailed the force changes during the on- and off-phase of the tetani, respectively. Independently of the stimulation rate, the half-times of the two signals were: on-phase, about 76 ms for force and 33 ms for MMG; off-phase, about 83 ms for force and 132 ms for MMG. There are two main comments to make about these results. First, during the on-phase the shortening of the contractile elements results at first in a muscle geometry change with low output force. After this, when the slack of the elastic-connective tissue has been taken up, the tension is efficiently transmitted to the tendon. Second, the different force and MMG dynamics in the on- and off-phases determine a counter-clockwise hysteresis with more force produced at a given muscle surface displacement during relaxation. To explain the results, the possible specific roles of some components of the muscle mechanical model, muscle mechanical properties and intra-muscular phenomena taking place during contraction have been discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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